Optical fiber is generally preferred as the transmission medium for communication networks because of the speed and bandwidth advantages associated with optical transmission. Wavelength division multiplexing (WDM), which combines many optical signals at different wavelengths for transmission in a single optical fiber, is being used to meet the increasing demands for more speed and bandwidth in optical transmission applications.
In communication networks, such as those employing WDM, individual optical signals may need to be selectively routed to different destinations. As is well known, a necessary component for selectively routing signals through interconnected nodes in a communication network is a high capacity matrix or cross-connect switch. At present, most cross-connect switches used in optical communication networks are either manual or electronic which require multiple optical-to-electrical and electrical-to-optical conversions. However, because of the speed and bandwidth advantages associated with transmitting information in optical form, all-optical network elements are emerging as the preferred solutions for WDM-based optical networks. Moreover, all-optical network elements are needed to provide the flexibility for managing bandwidth at the optical layer (e.g., on a wavelength by wavelength basis).
Although efforts have been made to develop all-optical cross-connects and switches, these efforts have not kept pace with the ever increasing demands for more speed and bandwidth. For example, some cross-connect arrangements have contemplated a combination of lithium niobate (LiNbO.sub.3) switch arrays with fiber amplifiers to address the speed and loss problems of prior systems. Although lithium niobate switch arrays provide fast switching capability and fiber amplifiers can compensate for the lossy characteristics of LiNbO.sub.3, these types of cross-connects do not provide the necessary wavelength selectivity for effectively managing bandwidth. In another type of optical cross-connect arrangement, wavelength channels are rearranged according to common destinations using wavelength-changing elements. In particular, multi-wavelength optical signals are demultiplexed into individual optical signals of different wavelengths and the individual optical signals are switched using separate layers of spatial switch fabric corresponding to each of the different wavelengths. The use of demultiplexers and separate layers of switch fabric results in this type of cross-connect arrangement being costly and complex to implement. Similarly, other types of optical cross-connect arrangements using multiple stages of switch fabric are also known to be costly and complex to implement.